Pixel structure having metal-insulator-semiconductor capacitor

ABSTRACT

A pixel structure including a scan line, a data line, an active device, a pixel electrode, a capacitor electrode line, a semi-conductive pattern layer and at least one dielectric layer is provided. The active device is electrically connected to the scan line and the data line. The pixel electrode is electrically connected to the active device. The capacitor electrode line is located under the pixel electrode. A first storage capacitor is formed between the capacitor electrode line and the pixel electrode. The semi-conductive pattern layer is disposed between the capacitor electrode line and the pixel electrode, the pixel electrode is electrically connected to the semi-conductive pattern layer. A second storage capacitor is formed between the semi-conductive pattern layer and the capacitor electrode line. The dielectric layer is disposed between the capacitor electrode line and the pixel electrode and located between the semi-conductive pattern layer and the capacitor electrode line.

CROSS-REFERENCE T0 RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 13/025,178, filed on Feb. 11, 2011, now allowed, which claims thepriority benefit of Taiwan application serial no. 99135459, filed onOct. 18, 2010. The entirety of each of the above-mentioned patentapplications is hereby incorporated by reference herein and made a partof this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a pixel structure and more particularly to apixel structure of a flat display.

2. Description of Related Art

An image sticking phenomenon of a flat display means an image or acontour of a previous static frame remains in a subsequent frame. Thatis, when a flat display displays a static frame persistently for a longperiod of time, an image or a contour from a previous static frameremains when a next frame is displayed.

Currently, in flat displays, liquid crystal displays are performed withan image sticking test before launching, for example. Conventionally,the image sticking test includes displaying a checkered black and whitepattern on a display panel for a long period of time and then switchingto a full screen with grayscale. If a sticking image of the checkeredblack and white pattern is shown on the full screen with the averagegrayscale, the image sticking phenomenon of the flat display is moreserious. In contrast, if the sticking image of the checkered black andwhite pattern is not shown on the full screen with the averagegrayscale, then the flat display has minimal or no image sticking atall.

As for the flat displays with the image sticking phenomenon, if theimage sticking phenomenon can be compensated or reduced with othermethods, the yield rate and the display quality of the flat displays canbe enhanced.

SUMMARY OF THE INVENTION

The invention is directed to a pixel structure capable of compensating abrightness difference caused by an image sticking phenomenon of a flatdisplay (especially of a flat display with a normally black drivingmethod) so as to reduce surface type image sticking of a flat display.

The invention is directed to a pixel structure including a scan line, adata line, an active device, a pixel electrode, a capacitor electrodeline, a semi-conductive pattern layer, and at least one dielectriclayer. The active device is electrically connected to the scan line andthe data line. The pixel electrode is electrically connected to theactive device. The capacitor electrode line is located underneath thepixel electrode. The capacitor electrode line and the pixel electrodeconstitute a first storage capacitor having a first storage capacitance.The semi-conductive pattern layer is disposed between the capacitorelectrode line and the pixel electrode. The pixel electrode iselectrically connected to the semi-conductive pattern layer. Thesemi-conductive pattern layer and the capacitor electrode lineconstitute a second storage capacitor having a second storagecapacitance. The at least one dielectric layer is disposed between thecapacitor electrode line and the pixel electrode and located between thesemi-conductive pattern layer and the capacitor electrode line.Especially, a sum of the first storage capacitance and the secondstorage capacitance is a total storage capacitance, and the secondstorage capacitance occupies 30%-80% of the total storage capacitance.

The invention is further directed to a pixel structure including a scanline, a data line, an active device, a pixel electrode, a capacitorelectrode line, a semi-conductive pattern layer, a reference electrodepattern layer, at least one dielectric layer, and a reference electrodeline. The active device is electrically connected to the scan line andthe data line. The pixel electrode is electrically connected to theactive device. The capacitor electrode line is located underneath thepixel electrode. The capacitor electrode line and the pixel electrodeconstitute a first storage capacitor having a first storage capacitance.The semi-conductive pattern layer is disposed between the capacitorelectrode line and the pixel electrode. The pixel electrode iselectrically insulated with the semi-conductive pattern layer. Thesemi-conductive pattern layer and the capacitor electrode lineconstitute a second storage capacitor having a second storagecapacitance. The reference electrode pattern layer is disposed betweenthe pixel electrode and the semi-conductive pattern layer. The referenceelectrode pattern layer is electrically insulated with the pixelelectrode and constitutes a third storage capacitor having a thirdstorage capacitance with the pixel electrode. The at least onedielectric layer is disposed between the capacitor electrode line andthe pixel electrode, disposed between the semi-conductive pattern layerand the capacitor electrode line, and disposed between the referenceelectrode pattern layer and the pixel electrode. The reference electrodeline is electrically connected to the reference electrode pattern layer.A sum of the first storage capacitance, the second storage capacitance,and the third storage capacitance is a total storage capacitance. Thesecond storage capacitance occupies 30%-80% of the total storagecapacitance.

In light of the foregoing, in the invention, the semi-conductive patternlayer is disposed in the pixel structure, so that the semi-conductivepattern layer and the capacitor electrode line constitute the storagecapacitor. The semi-conductive material changes the storage capacitanceof the storage capacitor under different operation frequencies anddifferent operation voltages. Thus, in the pixel structure, the storagecapacitance of the storage capacitor having the semi-conductive patternlayer occupies a certain ratio of the total storage capacitance so as tocompensate the brightness difference caused by the image stickingphenomenon of the flat display, thereby reducing the surface type imagesticking of the flat display.

In order to make the aforementioned and other features and advantages ofthe invention more comprehensible, several embodiments accompanied withfigures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide further understanding,and are incorporated in and constitute a part of this specification. Thedrawings illustrate exemplary embodiments and, together with thedescription, serve to explain the principles of the disclosure.

FIG. 1A illustrates a schematic top view of a pixel structure accordingto an embodiment of the invention.

FIG. 1B shows a schematic cross-sectional view taken along line A-A′ inFIG. 1A.

FIG. 2A illustrates a schematic top view of a pixel structure accordingto an embodiment of the invention.

FIG. 2B shows a schematic cross-sectional view taken along line B-B′ inFIG. 2A.

FIG. 3A illustrates a schematic top view of a pixel structure accordingto an embodiment of the invention.

FIG. 3B illustrates a schematic cross-sectional view taken along lineE-E′ and line F-F′ in FIG. 3A.

FIG. 4A illustrates a schematic top view of a pixel structure accordingto an embodiment of the invention.

FIG. 4B illustrates a schematic cross-sectional view taken along lineC-C′ and line D-D′ in FIG. 4A.

FIG. 5A shows a schematic top view of a pixel structure according to anembodiment of the invention.

FIG. 5B illustrates a schematic cross-sectional view taken along lineC-C′ and line D-D′ in FIG. 5A.

FIG. 6A illustrates a schematic top view of a pixel structure accordingto an embodiment of the invention.

FIG. 6B illustrates a schematic cross-sectional view taken along lineI-I′ and line II-II′ in FIG. 6A.

FIGS. 7 and 8 are diagrams showing a relationship between a ratio of astorage capacitance of a metal-insulator-semiconductor (MIS) storagecapacitor occupying a total storage capacitance and just noticedifference (JND).

FIG. 9 illustrates a relationship between voltage and change ofcapacitance.

DESCRIPTION OF EMBODIMENTS

FIG. 1A illustrates a schematic top view of a pixel structure accordingto an embodiment of the invention. FIG. 1B shows a schematiccross-sectional view taken along line A-A′ in FIG. 1A. Referring toFIGS. 1A and 1B, a pixel structure of the present embodiment includes ascan line SL, a data line DL, an active device T, a pixel electrode PE,a capacitor electrode line CL, a semi-conductive pattern layer 120, andat least one dielectric layer 110.

The scan line SL and the data line DL are disposed on a substrate 100.The scan line SL and the data line DL are disposed alternately. Aninsulation layer 102 is sandwiched between the scan line SL and the dataline DL. In other words, an extension direction of the data line DL isnot parallel to an extension direction of the scan line SL. Preferably,the extension direction of the data line DL is parallel to the extensiondirection of the scan line SL. The scan line SL and the data line SL aregenerally fabricated using a metal material for conductivity. However,the invention is not limited thereto. According to other embodiments,the scan line SL and the data line DL can also be fabricated using otherconductive material such as an alloy, a nitride of a metal material, anoxide of a metal material, an oxynitride of a metal material or othersuitable material, or a stacked layer of a metal material and otherconductive material.

The active device T is electrically connected to the scan line SL andthe data line DL. In details, the active device T has a gate G, a sourceS, and a drain D. The gate G is electrically connected to the scan lineSL and the source S is electrically connected to the data line DL. Theactive device T is a bottom gate thin film transistor (TFT) or a topgate TFT.

The pixel electrode PE is electrically connected to the active device T.In general, the drain D of the active device T is electrically connectedto the pixel electrode PE. The drain D of the active device T iselectrically connected to the pixel electrode PE directly or through acontact window. The pixel electrode PE is a transmissive pixelelectrode, a reflective pixel electrode, or a transflective pixelelectrode.

The capacitor electrode line CL is located underneath the pixelelectrode PE. The capacitor electrode line CL and the pixel electrode PEconstitute a first storage capacitor MII having a first storagecapacitance (Cst1). That is, the capacitor electrode line CL is adoptedas a bottom electrode of the first storage capacitor MII and the pixelelectrode PE is adopted as a top electrode of the first storagecapacitor MII. A first dielectric layer 102 and a second dielectriclayer 104 are disposed between the capacitor electrode line CL and thepixel electrode PE as a capacitor dielectric layer. In the presentembodiment, an extension direction of the capacitor electrode line CL isparallel to the extension direction of the scan line SL. The capacitorelectrode line CL is generally fabricated with a conductive material ora semi-conductive material for conductivity. The conductive material is,for example, a metal material such as aluminum, copper, silver, gold,titanium, molybdenum, tungsten, and so on. The semi-conductive materialis, for instance, poly-silicon, doped poly-silicon, or indium galliumzinc oxide, and so on. However, the invention is not limited thereto.According to other embodiments, the capacitor electrode line CL can alsobe fabricated using other conductive material such as an alloy, anitride of a metal material, an oxide of a metal material, an oxynitrideof a metal material or other suitable material, or a stacked layer of ametal material and other conductive material or semi-conductivematerial.

The semi-conductive pattern layer 120 is disposed between the capacitorelectrode line CL and the pixel electrode PE. The pixel electrode PE iselectrically connected to the semi-conductive pattern layer 120. Thesemi-conductive pattern layer 120 and the capacitor electrode line CLconstitute a second storage capacitor MIS having a second storagecapacitance (Cst2). That is, the capacitor electrode line CL is adoptedas a bottom electrode of the second storage capacitor MIS and thesemi-conductive pattern layer 120 is adopted as a top electrode of thesecond storage capacitor MIS. The first dielectric layer 102 is disposedbetween the capacitor electrode line CL and the semi-conductive patternlayer 120 as a capacitor dielectric layer. According to the presentembodiment, the semi-conductive pattern layer 120 includes a bottomsemi-conductive material layer 106 and a top ohmic contact materiallayer 108. The top ohmic contact material layer 108 is a dopedsemi-conductive material layer, for instance.

The dielectric layer 110 is disposed between the capacitor electrodeline CL and the pixel electrode PE and located between thesemi-conductive pattern layer 120 and the capacitor electrode line CL.In details, the dielectric layer 110 includes the first dielectric layer102 and the second dielectric layer 104. The first dielectric layer 102is sandwiched between the semi-conductive pattern layer 120 and thecapacitor electrode line CL. Thus, the first dielectric layer 102disposed between the semi-conductive pattern layer 120 and the capacitorelectrode line CL is adopted as a capacitor dielectric layer of thesecond storage capacitor MIS. The second dielectric layer 104 covers thefirst dielectric layer 102 and the semi-conductive pattern layer 120.Thus, the first dielectric layer 102 and the second dielectric layer 104are sandwiched between the pixel electrode PE and the capacitorelectrode line CL. In other words, the first dielectric layer 102 andthe second dielectric layer 104 sandwiched between the pixel electrodePE and the capacitor electrode line CL are adopted as a capacitordielectric layer of the first storage capacitor MII. Moreover, in thepresent embodiment, the second dielectric layer 108 has a contact windowC, so that the pixel electrode PE is electrically connected to thesemi-conductive pattern layer 120.

In particular, the second storage capacitance (Cst2) with a preferableratio is provided in the invention. In the present embodiment, a totalstorage capacitance (Cst-total) is the sum of the first storagecapacitance (Cst1) of the first storage capacitor MII and the secondstorage capacitance (Cst2) of the second storage capacitor MIS. Further,the second storage capacitance (Cst2) occupies 30%-80% of the totalstorage capacitance (Cst-total).

Generally, the capacitance of the capacitor is related to areas of topand bottom electrodes, voltages of the top and bottom electrodes, adielectric constant of the capacitor dielectric layer, and the thicknessof the capacitor dielectric layer. Therefore, in the invention, theareas and the voltages of the top and bottom electrodes can be adjusted,the capacitor dielectric layer with a specific dielectric constant canbe selected, and the thickness of the capacitor dielectric layer can beadjusted, so that the second storage capacitance (Cst2) occupies 30%-80%of the total storage capacitance (Cst-total). In details, in oneembodiment, an area overlapped by a bottom electrode (the capacitorelectrode line CL) and a top electrode (the pixel electrode PE) of thefirst storage capacitor MII and an area overlapped by a bottom electrode(the capacitor electrode line CL) and a top electrode (thesemi-conductive pattern layer 120) of the second storage capacitor MISare adjusted, so that the second storage capacitance (Cst2) occupies30%-80% of the total storage capacitance (Cst-total). According toanother embodiment, a dielectric material with a suitable dielectricconstant is selected to fabricate the capacitor dielectric layer (thedielectric layers 102, 104) of the first storage capacitor MII and thecapacitor dielectric layer (the dielectric layer 102) of the secondstorage capacitor MIS, such that the second storage capacitance (Cst2)occupies 30%-80% of the total storage capacitance (Cst-total). Inanother embodiment, the thickness of the capacitor dielectric layer (thedielectric layers 102, 104) of the first storage capacitor MII and thethickness of the capacitor dielectric layer (the dielectric layer 102)of the second storage capacitor MIS are adjusted, such that the secondstorage capacitance (Cst2) occupies 30%-80% of the total storagecapacitance (Cst-total).

Accordingly, the storage capacitor of the pixel structure of theinvention has the second storage capacitor MIS and the second storagecapacitance (Cst2) of the second storage capacitor MIS occupies 30%-80%of the total storage capacitance (Cst-total). Along with changes in theoperation voltage and operation frequency of the capacitor, thesemi-conductive pattern layer 120 in the second storage capacitor MISshows different capacitances in an accumulation region, a depletionregion, and an inversion region. When the semi-conductive pattern layer120 is in the accumulation region, the second storage capacitor MIS hasthe largest capacitance. When the semi-conductive pattern layer 120 isin the depletion region, the depletion region is expanded and reducedaccording to the change in the voltage, so that the capacitance of thesecond storage capacitor MIS changes. When the semi-conductive patternlayer 120 is in the inversion region, the second storage capacitor MIShas the smallest capacitance. Thus, with characteristics of changingwith the changes in the operation frequency and operation voltage, thestorage capacitance of the second storage capacitor MIS can compensatethe brightness difference caused by the image sticking phenomenon of theflat display so as to reduce surface type image sticking.

FIG. 2A illustrates a schematic top view of a pixel structure accordingto an embodiment of the invention. FIG. 2B shows a schematiccross-sectional view taken along line B-B′ in FIG. 2A. Embodimentsillustrated in FIGS. 2A and 2B are similar to the embodiments shown inFIGS. 1A and 1B; thus, elements identical as those in the embodiments ofFIGS. 1A and 1B are denoted with the same notations and further detailsare omitted hereinafter. The embodiments illustrated in FIGS. 2A and 2Bare different from the embodiments shown in FIGS. 1A and 1B in that thepixel structure in FIGS. 2A and 2B further includes a storage electrodepattern layer 130 disposed between the pixel electrode PE and thecapacitor electrode line CL. The storage electrode pattern layer 130 iselectrically connected to the pixel electrode PE. In details, in thisembodiment, the storage electrode pattern layer 130 covers thesemi-conductive pattern layer 120. In addition, the storage electrodepattern layer 130 is electrically connected to the pixel electrode PEthrough the contact window C formed in the second dielectric layer 104.

In particular, in the present embodiment, other than the first storagecapacitor MII and the second storage capacitor MIS, the storageelectrode pattern layer 130 and the capacitor electrode line CL furtherconstitute a third storage capacitor MIM having a third storagecapacitance (Cst3). That is, the capacitor electrode line CL is adoptedas a bottom electrode of the third storage capacitor MIM, the storageelectrode pattern layer 130 is adopted as a top electrode of the thirdstorage capacitor MIM, and the first dielectric layer 102 sandwichedbetween the storage electrode pattern layer 130 and the capacitorelectrode line CL is adopted as a capacitor dielectric layer of thethird storage capacitor MIM.

Therefore, the total storage capacitance (Cst-total) of the pixelstructure in the present embodiment is the sum of the first storagecapacitance (Cst1) of the first storage capacitor MIL the second storagecapacitance (Cst2) of the second storage capacitor MIS, and the thirdstorage capacitance (Cst3) of the third storage capacitor MIM. Moreover,the second storage capacitance (Cst2) occupies 30%-80% of the totalstorage capacitance (Cst-total).

Similarly, in the present embodiment, areas overlapped by the bottomelectrodes and the top electrodes, voltages of the top and the bottomelectrodes, dielectric constants of the capacitor dielectric layers, andthicknesses of the capacitor dielectric layers of the first storagecapacitor MIL the second storage capacitor MIS, and the third storagecapacitor MIM can be adjusted, so that the second storage capacitance(Cst2) of the second storage capacitor MIS occupies 30%-80% of the totalstorage capacitance (Cst-total).

For example, as depicted in FIGS. 2A and 2B, the area of thesemi-conductive pattern layer 120 is designed to be smaller than thearea of the storage electrode pattern layer 130. Thus, other thancovering an upper surface of the semi-conductive pattern layer 120, thestorage electrode pattern layer 130 also covers a side surface of thesemi-conductive pattern layer 120. In other words, in the presentembodiment, the area of the electrodes in the storage capacitor isspecifically designed so that the second storage capacitance (Cst2) ofthe second storage capacitor MIS occupies 30%-80% of the total storagecapacitance (Cst-total).

FIG. 3A illustrates a schematic top view of a pixel structure accordingto an embodiment of the invention. FIG. 3B illustrates a schematiccross-sectional view taken along line E-E′ and line F-F in FIG. 3A.Embodiments illustrated in FIGS. 3A and 3B are similar to theembodiments shown in FIGS. 2A and 2B; thus, elements identical as thosein the embodiments of FIGS. 2A and 2B are denoted with the samenotations and further details are omitted hereinafter. The embodimentsin FIGS. 3A and 3B are different from those in FIGS. 2A and 2B in thatthe storage electrode pattern layer 130 and the semi-conductive patternlayer 120 are not overlapped in FIGS. 3A and 3B, and the storageelectrode pattern layer 130 and the semi-conductive pattern layer 120are electrically connected to the pixel electrode PE respectively.Furthermore, the second dielectric layer 104 has a first contact windowC1 and a second contact window C2. The first contact window C1 iselectrically connected to the storage electrode pattern layer 130 andthe pixel electrode PE. The second contact window C2 is electricallyconnected to the semi-conductive pattern layer 120 and the pixelelectrode PE.

Similarly, in the present embodiment, areas overlapped by the bottomelectrodes and the top electrodes, voltages of the top and the bottomelectrodes, dielectric constants of the capacitor dielectric layers, andthicknesses of the capacitor dielectric layers of the first storagecapacitor MII, the second storage capacitor MIS, and the third storagecapacitor MIM are adjusted, so that the second storage capacitance(Cst2) of the second storage capacitor MIS occupies 30%-80% of the totalstorage capacitance (Cst-total).

FIG. 4A illustrates a schematic top view of a pixel structure accordingto an embodiment of the invention. FIG. 4B illustrates a schematiccross-sectional view taken along line C-C′ and line D-D′ in FIG. 4A.Referring to FIGS. 4A and 4B, a pixel structure of the presentembodiment includes a scan line SL, a plurality of data lines DL1, DL2,a plurality of active devices T1, T2, a plurality of pixel electrodesPE1, PE2, a plurality of capacitor electrode lines CL1, CL2, a pluralityof semi-conductive pattern layers 120 a, 120 b, a plurality of storageelectrode pattern layers 130 a, 130 b, and a dielectric layer 110.

The active device T1 has a gate G1, a source S1, and a drain D1. Thegate G1 is electrically connected to the scan line SL and the source S1is electrically connected to the data line DL1. The active device T2 hasa gate G2, a source S2, and a drain D2. The gate G2 is electricallyconnected to the scan line SL and the source S2 is electricallyconnected to the data line DL2. The active devices T1, T2 are bottomgate TFTs or top gate TFTs.

The drain D1 of the active device T1 is electrically connected to thepixel electrode PE1 and the drain D2 of the active device T2 iselectrically connected to the pixel electrode PE2. The pixel electrodesPE1, PE2 are transmissive pixel electrodes, reflective pixel electrodes,or transflective pixel electrodes respectively.

The capacitor electrode line CL1 is located underneath the pixelelectrode PE1. The capacitor electrode line CL2 is located underneaththe pixel electrode PE2. The capacitor electrode line CL1 and the pixelelectrode PE1 constitute a first storage capacitor MII-1 having a firststorage capacitance (Cst1-1). The capacitor electrode line CL2 and thepixel electrode PE2 constitute a first storage capacitor MII-2 (notshown) having a first storage capacitance (Cst1-2).

The semi-conductive pattern layer 120 a is sandwiched between thecapacitor electrode line CL1 and the pixel electrode PE1. Thesemi-conductive pattern layer 120 a and the capacitor electrode line CL1constitute a second storage capacitor MIS-1 having a second storagecapacitance (Cst2-1). According to the present embodiment, thesemi-conductive pattern layer 120 a includes a bottom semi-conductivematerial layer 106 a and a top ohmic contact material layer 108 a.Similarly, the semi-conductive pattern layer 120 b is sandwiched betweenthe capacitor electrode line CL2 and the pixel electrode PE2. Thesemi-conductive pattern layer 120 b and the capacitor electrode line CL2constitute a second storage capacitor MIS-2 having a second storagecapacitance (Cst2-2). According to the present embodiment, thesemi-conductive pattern layer 120 b includes a bottom semi-conductivematerial layer 106 b and a top ohmic contact material layer 108 b.

The storage electrode pattern layer 130 a is sandwiched between thepixel electrode PE1 and the capacitor electrode line CL1, and thestorage electrode pattern layer 130 a and the pixel electrode PE1 areelectrically connected. Additionally, the storage electrode patternlayer 130 a and the capacitor electrode line CL1 constitute a thirdstorage capacitor MIM-1 having a third storage capacitance (Cst3-1).Similarly, the storage electrode pattern layer 130 b is sandwichedbetween the pixel electrode PE2 and the capacitor electrode line CL2,and the storage electrode pattern layer 130 b and the pixel electrodePE2 are electrically connected. Further, the storage electrode patternlayer 130 b and the capacitor electrode line CL2 constitute a thirdstorage capacitor MIM-2 having a third storage capacitance (Cst3-2).

The dielectric layer 110 includes a first dielectric layer 102 and asecond dielectric layer 104. The first dielectric layer 102 issandwiched between the semi-conductive pattern layer 120 a and thecapacitor electrode line CL1 and between the semi-conductive patternlayer 120 b and the capacitor electrode line CL2. Here, the firstdielectric layer 102 is adopted as capacitor dielectric layers of thesecond storage capacitors MIS-1, MIS-2. The second dielectric layer 104covers the first dielectric layer 102 and the semi-conductive patternlayers 120 a, 120 b. Thus, the first dielectric layer 102 and the seconddielectric layer 104 are sandwiched between the pixel electrode PE1 andthe capacitor electrode line CL1 and between the pixel electrode PE2 andthe capacitor electrode line CL2. Therefore, the first dielectric layer102 and the second dielectric layer 104 are adopted as capacitordielectric layers of the first storage capacitors MII-1, MII-2. Thefirst dielectric layer 102 is further sandwiched between the storageelectrode pattern layer 130 a and the capacitor electrode line CL1 andbetween the storage capacitor pattern layer 130 b and the capacitorelectrode line CL2. Here, the first dielectric layer 102 is adopted ascapacitor dielectric layers of the third storage capacitors MIM-1,MIM-2. Also, in the present embodiment, the second dielectric layer 108has contact windows C1, C2, so that the pixel electrode PE1 and thestorage electrode pattern layer 130 a are electrically connected and thepixel electrode PE2 and the storage electrode pattern layer 130 b areelectrically connected.

In particular, a sum of the first storage capacitances (Cst1-1, Cst1-2)of the first storage capacitors MII-1, MII-1, the second storagecapacitances (Cst2-1, Cst2-2) of the second storage capacitors MIS-1,MIS-2, and the third storage capacitances (Cst3-1, Cst3-2) of the thirdstorage capacitors MIM-1, MIM-2 is a total storage capacitance(Cst-total). Moreover, the second storage capacitances (Cst2-1, Cst2-2)occupy 30%-80% of the total storage capacitance (Cst-total). Similarly,in the present embodiment, areas overlapped by the bottom electrodes andthe top electrodes, voltages of the top and the bottom electrodes,dielectric constants of the capacitor dielectric layers, and thicknessesof the capacitor dielectric layers of the first storage capacitorsMII-1, MII-2, the second storage capacitor MIS-1, MIS-2, and the thirdstorage capacitor MIM-1, MIM-2 are adjusted, so that the second storagecapacitances (Cst2-1, Cst2-2) of the second storage capacitors MIS-1,MIS-2 occupy 30%-80% of the total storage capacitance (Cst-total).

FIG. 5A shows a schematic top view of a pixel structure according to anembodiment of the invention. FIG. 5B illustrates a schematiccross-sectional view taken along line C-C′ and line D-D′ in FIG. 5A.Embodiments illustrated in FIGS. 5A and 5B are similar to theembodiments shown in FIGS. 4A and 4B; thus, elements identical as thosein the embodiments of FIGS. 4A and 4B are denoted with the samenotations and further details are omitted hereinafter. The embodimentsin FIGS. 5A and 5B are different from those depicted in FIGS. 4A and 4Bin that the storage electrode pattern layer is not disposed above thecapacitor electrode line CL1 and only the semi-conductive pattern layer120 a is disposed above the capacitor electrode line CL1. Moreover, thepixel electrode PE1 and the semi-conductive pattern layer 120 areelectrically connected through the contact window C1. Further, thesemi-conductive pattern layer is not disposed above the capacitorelectrode line CL2 and only the storage electrode pattern layer 130 b isdisposed above the capacitor electrode line CL2. Also, the pixelelectrode PE2 and the storage electrode pattern layer are electricallyconnected through the contact window C2.

Therefore, in the present embodiment, the capacitor electrode line CL1and the pixel electrode PE1 constitute the first storage capacitor MII-1having the first storage capacitance (Cst1-1). The capacitor electrodeline CL2 and the pixel electrode PE2 constitute the first storagecapacitor MII-2 (not shown) having the first storage capacitance(Cst1-2). The semi-conductive pattern layer 120 and the capacitorelectrode line CL1 constitute the second storage capacitor MIS havingthe second storage capacitance (Cst2). The storage electrode patternlayer 130 b and the capacitor electrode line CL2 constitute the thirdstorage capacitor MIM having a third storage capacitance (Cst3).

Specifically, a sum of the first storage capacitances (Cst1-1, Cst1-2)of the first storage capacitors MII-1, MII-1, the second storagecapacitance (Cst2) of the second storage capacitor MIS, and the thirdstorage capacitance (Cst3) of the third storage capacitor MIM is a totalstorage capacitance (Cst-total). Moreover, the second storagecapacitance (Cst2) occupies 30%-80% of the total storage capacitance(Cst-total).

FIG. 6A illustrates a schematic top view of a pixel structure accordingto an embodiment of the invention. FIG. 6B illustrates a schematiccross-sectional view taken along line I-I′ and line II-II′ in FIG. 6A.Embodiments illustrated in FIGS. 6A and 6B are similar to theembodiments shown in FIGS. 1A and 1B; thus, elements same as those inthe embodiments of FIGS. 1A and 1B are denoted with the same notationsand further details are omitted hereinafter. The embodiments in FIGS. 6Aand 6B are different from those in FIGS. 1A and 1B in that the pixelstructure further includes a reference electrode pattern layer 140 and areference electrode line RL.

The reference electrode pattern layer 140 is sandwiched between thepixel electrode PE and the semi-conductive pattern layer 120. Thereference electrode pattern layer 140 is electrically insulated with thepixel electrode PE. In addition, the reference electrode pattern layer140 and the pixel electrode PE constitute a third storage capacitor MII′having a third storage capacitance (Cst3). In the present embodiment,the reference electrode pattern layer 140 covers the semi-conductivepattern layer 120.

The reference electrode line RL is electrically connected to thereference electrode pattern layer 140. In the present embodiment, thereference electrode line RL and the capacitor electrode line CL aredisposed in the same layer. However, the invention is not limitedthereto.

In the present embodiment, the first dielectric layer 102 is sandwichedbetween the semi-conductive pattern layer 120 and the capacitorelectrode line CL. The second dielectric layer 104 covers the firstdielectric layer 102 and the reference electrode pattern layer 140.Thus, the first dielectric layer 102 and the second dielectric layer 104are sandwiched between the pixel electrode PE and the capacitorelectrode line CL. The second dielectric layer 104 is sandwiched betweenthe pixel electrode PE and the reference electrode pattern layer 140. Inthe present embodiment, the reference electrode pattern layer 140 andthe reference electrode line RL are electrically connected through acontact window C3 formed in the second dielectric layer 104, a contactwindow C4 formed in the first dielectric layer 102 and the seconddielectric layer 104, and a connecting layer 150 disposed on the seconddielectric layer 102. In details, the contact window C3 is electricallyconnected to the reference electrode pattern layer 140 and theconnecting layer 150, and the contact window C4 is electricallyconnected to the reference electrode line RL and the connecting layer150, such that the reference electrode pattern layer 140 is electricallyconnected to the reference electrode line RL. The connecting layer 150is electrically connected to the pixel electrode PE. Accordingly, thereference electrode pattern layer 140 is electrically connected to thepixel electrode PE. In the present embodiment, the connecting layer 150and the pixel electrode PE are disposed in the same layer; however, aspace is present therebetween for the connecting layer 150 and the pixelelectrode PE to be electrically insulated.

As aforementioned, in the present embodiment, the capacitor electrodeline CL and the pixel electrode PE constitute the first storagecapacitor MII having the first storage capacitance (Cst1). Thesemi-conductive pattern layer 120 and the capacitor electrode line CL1constitute the second storage capacitor MIS having the second storagecapacitance (Cst2). The reference electrode pattern layer 140 and thepixel electrode PE constitute the third storage capacitor MII′ havingthe third storage capacitance (Cst3). Since the reference electrodepattern layer 140 is electrically connected to the reference electrodeline RL, the third storage capacitance (Cst3) of the third storagecapacitor MII′ and the second storage capacitance (Cst2) of the secondstorage capacitor MIS can be changed by adjusting the voltages of thereference electrode line RL.

Similarly, the total storage capacitance (Cst-total) of the pixelstructure in the present embodiment is the sum of the first storagecapacitance (Cst1) of the first storage capacitor MII, the secondstorage capacitance (Cst2) of the second storage capacitor MIS, and thethird storage capacitance (Cst3) of the third storage capacitor MILHere, the second storage capacitance (Cst2) occupies 30%-80% of thetotal storage capacitance (Cst-total).

In the present embodiment, the capacitance value of the third storagecapacitance (Cst3) of the third storage capacitor MII′ and the secondstorage capacitance (Cst2) of the second storage capacitor MIS can becontrolled by adjusting the voltage of the reference electrode line RL.Also, areas of the top and bottom electrodes, dielectric constants ofthe capacitor dielectric layers, and thicknesses of the capacitordielectric layers of the first storage capacitor MII, the second storagecapacitor MIS, and the third storage capacitor MII′ are adjusted, sothat the second storage capacitance (Cst2) of the second storagecapacitor MIS occupies 30%-80% of the total storage capacitance(Cst-total).

FIGS. 7 and 8 are diagrams showing a relationship between a ratio of astorage capacitance of a metal-insulator-semiconductor (MIS) storagecapacitor occupying a total storage capacitance and a just noticedifference (JND). In FIGS. 7 and 8, the horizontal axis represents theratio of the storage capacitance of the MIS storage capacitor occupyingthe total storage capacitance while the vertical axis represents the JNDvalue. Referring to FIG. 7, as the JND value becomes smaller, thevoltage compensated by the capacitance becomes higher. The curve 710shows a firing time of an image sticking test to be 504 hours and thecurve 720 shows a firing time of an image sticking test to be 168 hours.As shown in FIG. 7, when the storage capacitance of the MIS storagecapacitor occupies 20%-80% of the total storage capacitance, the JNDvalue thereof is smaller. The image sticking test of FIG. 8 is performedunder low grayscale (level 32) and the curve 810 shows a firing time ofan image sticking test to be 504 hours and the curve 820 shows a firingtime of an image sticking test to be 168 hours. As illustrated in FIG.8, when the storage capacitance of the MIS storage capacitor occupies30%-80% of the total storage capacitance, the JND value thereof issmaller. Thus, as depicted in FIGS. 7 and 8, when the storagecapacitance of the MIS storage capacitor in the pixel structure occupies30%-80% of the total storage capacitance, the JND value is morepreferable. In other words, when the storage capacitance of the MISstorage capacitor occupies 30%-80% of the total storage capacitance, thecapacitance of the MIS storage capacitor better compensates the imagesticking phenomenon of the liquid crystal display. The invention is notlimited to liquid crystal displays, but can also compensate other flatdisplays such as organic light emitting displays or electrophoreticdisplays.

FIG. 9 illustrates a relationship between voltage and change ofcapacitance. In FIG. 9, a horizontal axis represents voltage (V) while avertical axis represents capacitance. Further, the curve 910 shows arelationship between the voltage and the capacitance of ametal-insulator-metal (MIM) capacitor with an operation frequency of 100Hz; the curve 920 shows a relationship between the voltage and thecapacitance of the MIM capacitor with an operation frequency of 100 KHz;the curve 930 shows a relationship between the voltage and thecapacitance of the MIS capacitor with an operation frequency of 100 Hz;and the curve 940 shows a relationship between the voltage and thecapacitance of the MIS capacitor with an operation frequency of 100 KHz.As depicted in FIG. 9, whether the MIM capacitor is operated with a lowfrequency or a high frequency, the capacitance thereof does not varywith the change of the operation voltage. On the other hand, whether theMIS capacitor is operated with a low frequency or a high frequency, thecapacitance thereof varies with the change of the operation voltage.

Referring to FIG. 9, a semi-conductive material is adopted forfabricating the electrodes of the MIS capacitor and as thesemi-conductive material includes the accumulation region, the depletionregion, and the inversion region due to the different operation voltagesand operation frequencies, the capacitor can provide differentcapacitances in the accumulation region, the depletion region, and theinversion region of the semi-conductive material. Conversely, in the MIMcapacitor, the top and the bottom electrodes of the capacitor are bothfabricated with metal instead of the semi-conductive material.Consequently, the capacitance of the MIM capacitor does not providedifferent capacitances due to different operation voltages and operationfrequencies.

In summary, in the invention, the semi-conductive pattern layer isdisposed in the pixel structure, so that the semi-conductive patternlayer and the capacitor electrode line constitute the storage capacitor.The semi-conductive material changes the storage capacitance of thestorage capacitor under different operation frequencies and operationvoltages. Thus, in the pixel structure, the storage capacitance of thestorage capacitor having the semi-conductive pattern layer occupies acertain ratio of the total storage capacitance so as to compensate thebrightness difference caused by the image sticking phenomenon of theflat display (especially the flat display with the normally blackdriving method), thereby reducing the surface type image sticking of theflat display.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of thedisclosed embodiments without departing from the scope or spirit of thedisclosure. In view of the foregoing, it is intended that the disclosurecover modifications and variations of this disclosure provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. A pixel structure, comprising: a scan line and adata line; an active device, electrically connected to the scan line andthe data line; a pixel electrode, electrically connected to the activedevice; a capacitor electrode line, located underneath the pixelelectrode, wherein the capacitor electrode line and the pixel electrodeconstitute a first storage capacitor having a first storage capacitance;a semi-conductive pattern layer, disposed between the capacitorelectrode line and the pixel electrode, wherein the pixel electrode iselectrically connected to the semi-conductive pattern layer, and thesemi-conductive pattern layer and the capacitor electrode lineconstitute a second storage capacitor having a second storagecapacitance; a reference electrode pattern layer, disposed between thepixel electrode and the semi-conductive pattern layer, wherein thereference electrode pattern layer is electrically insulated with thepixel electrode and constitutes a third storage capacitor having a thirdstorage capacitance with the pixel electrode; at least one dielectriclayer, disposed between the capacitor electrode line and the pixelelectrode, disposed between the semi-conductive pattern layer and thecapacitor electrode line, and disposed between the reference electrodepattern layer and the pixel electrode, wherein the at least onedielectric layer comprises: a first dielectric layer, disposed betweenthe semi-conductive pattern layer and the capacitor electrode line; anda second dielectric layer, covering the first dielectric layer and thereference electrode pattern layer, wherein the first dielectric layerand the second dielectric layer are sandwiched between the pixelelectrode and the capacitor electrode line, and the second dielectriclayer is sandwiched between the pixel electrode and the referenceelectrode pattern layer; a reference electrode line, electricallyconnected to the reference electrode pattern layer, a first contactwindow, disposed in the second dielectric layer; a second contactwindow, disposed in the first dielectric layer and the second dielectriclayer; and a connecting layer, electrically connected to the referenceelectrode pattern layer and the reference electrode line respectivelythrough the first contact window and the second contact window, suchthat the reference electrode pattern layer and the reference electrodeline are electrically connected, wherein a total storage capacitance isthe sum of the first storage capacitance, the second storage capacitanceand the third storage capacitance, and the second storage capacitanceoccupies 30%-80% of the total storage capacitance.
 2. The pixelstructure as claimed in claim 1, wherein the reference electrode lineand the capacitor electrode line are disposed in a same layer.
 3. Thepixel structure as claimed in claim 1, wherein the reference electrodepattern layer covers the semi-conductive pattern layer.